The present invention is directed to ink compositions and to processes for the preparation and use thereof. More specifically, the present invention is directed to compositions suitable for use in ink jet printing processes. One embodiment of the present invention is directed to an ink composition which comprises (a) water; (b) a colorant selected from the group consisting of reactive dyes having terminal vinyl sulfate groups and mixtures thereof; (c) N,N'-bis(3-aminopropyl)-1,2-ethylenediamine; (d) imidazole; (e) phosphorous acid or a phosphite salt; (f) tripropylene glycol monomethyl ether; and (g) a salt selected from Zn.sup.2+ salts and mixtures thereof.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 5,254,159 (Gundlach et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, an anionic dye, and a compound selected from the group consisting of N,N'-bis(3-aminopropyl)-1,2-ethylenediamine, 1,4-bis(3-aminopropyl)piperazine, N,N'-bis(3-aminopropyl)-1,3-propanediamine, N,N'-bis(2-amionethyl)-1,3-propanediamine, N,N'-bis(3-aminopropyl)-1,4-butanediamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, nitrilotrisethylamine, N,N'-(diaminoethyl)piperazine, piperazinylethylethylenediamine, aminoethyltriethylenetetramine, aminoethylpiperazinylethylethylenediamine, piperazinylethyldiethylenetriamine, pentaethylene hexamine, and mixtures thereof, said ink composition having a pH of more than about 8 and less than about 9. Further disclosed is an ink composition comprises water, a dye, a polyamine compound, and a monoamine compound. In one embodiment, the polyamine compound is a first generation dendrimer compound having terminal primary amine groups.
U.S. Pat. No. 5,389,131 (Colt et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing an ink composition which comprises (a) forming a mixture by admixing water and a base; (b) adding a colorant to the mixture; and (c) adjusting the pH of the mixture by adding phosphorous acid thereto. Also disclosed is a process for preparing an ink composition which comprises (a) forming a mixture by admixing water and phosphorous acid; (b) adding a colorant to the mixture; and (c) adjusting the pH of the mixture by adding a base thereto. Further disclosed are ink compositions prepared by these processes. One embodiment is directed to an ink composition which comprises water, a colorant, and phosphorous acid. Another embodiment of the invention is directed to an ink composition which comprises water, a colorant, and a phosphite salt. Additionally disclosed are processes which comprise incorporating these inks into an ink jet printing apparatus and causing droplets of the ink to be ejected in an imagewise pattern onto a substrate. The presence of phosphorous acid and the base create a buffer system in the ink which adjusts the ink to the desired pH, and also enables improved latency, recoverability, and waterfastness.
U.S. Pat. No. 5,300,143 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, a water soluble dye, a first component selected from the group consisting of sulfones and mixtures thereof, and a second component selected from the group consisting of cyclic amines having at least one hydrogen atom bonded to a nitrogen atom, cyclic amides having at least one hydrogen atom bonded to a nitrogen atom, diamides having at least one hydrogen atom bonded to a nitrogen atom, polyalkoxy-substituted amides having at least one hydrogen atom bonded to a nitrogen atom, polyimine-substituted amides having at least one hydrogen atom bonded to a nitrogen atom, and mixtures thereof. Also disclosed is an ink jet printing process employing these inks.
U.S. Pat. No. 5,223,026 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses a thermal ink jet printing process which comprises incorporating into a thermal ink jet printing apparatus an ink composition comprising a colorant and a liquid vehicle which comprises a mixture of water and an organic component selected from the group consisting of: (1) cyclic amides; and mixtures thereof; and heating selected nozzles in the printing apparatus containing the ink, thereby causing droplets of the ink to be ejected in an imagewise pattern onto a substrate.
U.S. Pat. No. 5,488,402 and U.S. Pat. No. 5,428,383 (Shields et al.), the disclosures of each of which are totally incorporated herein by reference, disclose a method for controlling color bleed in multi-color thermal ink jet printing systems. Color bleed involves the migration of coloring agents between adjacent zones in a multi-color printed image on a substrate. To control color bleed between any two ink compositions in a multi-ink system, at least one of the ink compositions will contain a precipitating agent (e.g. a multi-valent metal salt). The precipitating agent is designed to react with the coloring agent in the other ink composition of concern. As a result, when the two ink compositions come in contact, a precipitate is formed from the coloring agent in the other ink composition which prevents migration thereof and color bleed problems. This technique is applicable to printing systems containing two or more ink compositions, and enables distinct multi-color images to be produced without the problems normally caused by color bleed.
While known compositions and processes are suitable for their intended purposes, a need remains for improved ink compositions suitable for use in thermal ink jet printing processes. In addition, a need remains for ink compositions which exhibit improved waterfastness. Further, a need remains for ink compositions which exhibit reduced intercolor bleed. Additionally, a need remains for ink compositions which exhibit improved color quality. There is also a need for magenta ink compositions which exhibit improved color quality. In addition, there is a need for ink compositions which exhibit reduced wet smear.